The present invention relates generally to stators for dynamoelectric machines and, in particular, to an stator winding for a dynamoelectric machine having cascaded end loops and an increased cooling surface area.
Dynamoelectric machines, such as alternating current electric generators, or alternators, are well known. Prior art alternators typically include a stator assembly and a rotor assembly disposed in an alternator housing. The stator assembly is mounted to the housing and includes a generally cylindrically-shaped stator core having a plurality of slots formed therein. The rotor assembly includes a motor rotor attached to a generally cylindrical shaft that is rotatably mounted in the housing and is coaxial with the stator assembly. The stator assembly includes a plurality of wires wound thereon, forming windings.
In one relatively new type of stator known as a high slot fill stator, the stator windings are formed of substantially straight portions that are located in the slots and end loop sections that connect two adjacent straight portions of the same phase and are formed in a predetermined multi-phase (e.g. three or six) winding pattern in the slots of the stator core. The rotor assembly typically includes opposed poles as part of claw fingers that are positioned around an electrically charged rotor coil. The rotor coil produces a magnetic field. When a prime mover, such as a steam turbine, a gas turbine, or a drive belt from an automotive internal combustion engine, rotates the rotor assembly, the magnetic field of the rotor assembly passes through the stator windings, inducing an alternating electrical current in the stator windings in a well known manner. The alternating electrical current is then routed from the alternator to a distribution system for consumption by electrical devices or, in the case of an automotive alternator, to a rectifier and then to a charging system for an automobile battery.
The high slot fill stator is characterized by rectangular core slots and rectangular shaped conductors. The width, including any insulation, of the rectangular shaped conductors fit closely to the width, including any insulation, of the rectangular core slots. High slot fill stators are advantageous because they are efficient and help produce more electrical power per winding than other types of prior art stators. These stators, however, are disadvantageous because the windings are typically interlaced, in which the wires are required to alternate between outer and inner radial layers of each slot. These interlaced windings require an interlacing process to interlace the conductors of all the phases prior to inserting the winding into the core and therefore disadvantageously increase the complexity of placing the winding the stator. Other prior art stators have utilized hairpin conductors, in which separate U-shaped conductor pieces are placed in the core slots from an upper or lower axial end of the stator core and then welded together. While the hairpin conductors are not interlaced, the difficulty of manufacturing the stators is still increased because the opposing ends of the U-shaped conductors must be welded to form the stator winding.
During operation of the alternator, the stator windings increase in temperature as a result of the induced electrical current flowing through the winding resistance. As the stator windings increase in temperature, the efficiency of the alternator disadvantageously decreases.
It is desirable, therefore, to provide a stator having a winding that meets the requirements of a high slot fill stator but does not require the complex interlaced winding process or the hairpin conductors of the prior art. It is also desirable to provide a stator for a dynamoelectric machine that can provide improved cooling for the stator winding.
A stator winding for a dynamoelectric machine, such as an alternator, having cascaded end loops and increased cooling surface area is adapted to be placed in a plurality of circumferentially spaced axially-extending core slots in a surface of a generally cylindrically-shaped stator core. The stator winding includes a plurality of substantially straight segments alternately connected at the first and second ends of the stator core by a plurality of end loops or end loop segments to form the winding. The end loops include first and second sloped sides meeting at an apex portion. The first and second sloped sides include at least one body 25 portion offset in opposite radial directions. Each of the end loop segments form a cascaded winding pattern allowing sequential phase insertion, defined in more detail below and causing no interference between the end loop segments of each of the phases and providing increasing cooling surface area for the winding.
Preferably, the stator winding in accordance with the present invention advantageously provides improved cooling by shifting a predetermined number of phases to provide increased cooling surface area.
Preferably, the straight segments have a first cross-sectional shape wherein the area of the first cross-sectional shape of the straight segments is preferably substantially equal to the area of the cross-sectional shape of the end loop segments.
Alternatively, the area of the cross-sectional shape of the straight segments is substantially double the area of the cross-sectional shape of the end loop segments.